The SR 232 OV/SD/CL/HC/HF chemical cartridge is used together with Sundstrom half masks and full face masks Air Purifying Respirator (APR) to provide protection against the following types of gases and vapors: OV protects against Organic vapors. SD protects against Sulfur dioxide. CL protects against Chlorine. HC protects against Hydrogen chloride. HF protects against Hydrogen fluoride. For chimney service work, this filter should be combined with a SR 510 Particulate filter.